Liquid crystal light valves (LCLVs) generally employ cells containing liquid crystal molecules. When the ordering of the liquid crystal molecules in regions of the cell is changed (for example, by means of a local electric field), the optical properties of those regions also change. Examples of LCLVs are disclosed in U.S. Pat. Nos. 4,728,174 and 4,826,293. Generally, a LCLV includes a layer of liquid crystal enclosed in a cell formed by insulating films on either side to provide electrical and chemical isolation. Optical images can thus be produced by a spatial voltage pattern applied to the device.
In LCLV displays, topographic projections ("bumps") are used to keep neighboring planar surfaces at a fixed distance apart from one another. The liquid crystal thickness of LCLV, which is critical to the device performance, is traditionally maintained by using plastic shim spacers (cutout sheets of plastic) or evaporated dots of silicon monoxide "posts". Each post is large in scale (typically one millimeter in diameter or larger) and restricted to use around the outer edges of the device. A thickness variation thus results if the surfaces of the device are not precisely flat. In an alternative spacing method, small glass beads (typically between 3 to 4 micrometers in diameter) are strewn onto a sublayer to serve as spacers. This method is deficient in that the locations where the glass beads finally land cannot be predetermined, so the distribution pattern of the beads cannot be controlled. Further, although the glass beads are relatively small, they tend to clump together into larger lumps which cast shadows, i.e. artifacts, onto the LCLV read-out.
A membrane probe is used for testing integrated circuits. An example of a membrane probe and the apparatus utilizing it are disclosed in U.S. Pat. Nos. 5,313,157 and 5,148,103, respectively. Such a probe comprises a flexible membrane having a pattern of electrically conductive traces formed on one side of the membrane, and a plurality of contact pads on selected ones of the traces to provide a temporary electrical connection to the circuit under test. Connector pads on the other side of the membrane are connected electrically to the traces to facilitate rapid detachable electric connection to a test fixture.
In membrane probe devices for testing integrated circuits, small projections (of about 3 to 6 .mu.m in diameter, and 25 to 50 .mu.m in height) are used to assure that a low resistance electrical contact is made at precise locations over distributed surfaces. There are several conventional ways to fabricate the projections on membrane probes. In one process disclosed in U.S. Pat. No. 5,197,184, the projecting contacts are produced as a mold on a metallic plate. Polyimide isolating layers and metal interconnecting layers are laminated and delineated to build up the test probe. This multilayer sheet is then demounted from the metal plate and attached to a stiffer substrate with the center removed to provide a tight membrane that can be deflected by air pressure or mechanically to contact the integrated circuits (ICs) under test. An alternative process has been used in which a photoresist mask is prepared with holes where the contact metal will be electroplated up to form the projection. These projections are generally flat-topped and make a relatively poor contact with the IC. These projections are difficult to prepare in diameters less than about 100 .mu.m. Moreover, due to their small sizes, the adherence of the contact metal to the metal traces is poor. In yet another process, the contact pads on the signal traces are made by depositing a thick metal film and etching away the excess metal around the projection. This is a slow and costly process.